1. Field of the Invention
This invention relates generally to a valve actuating apparatus for engines, and more particularly concerns a system for actuating and controlling reciprocating valves for the cylinders of an internal combustion engine.
2. Description of Related Art
Conventional piston type internal combustion engines typically utilize mechanically driven camshafts for operation of intake and exhaust valves, with fixed valve lift and return timing and duration. Electrically or hydraulically controlled valves for improved control of valve operation have also been used in order to improve fuel economy and reduce exhaust emissions.
For example, a variable engine valve control system is known in which each of the reciprocating intake or exhaust valves is hydraulically controlled, and includes a piston receiving fluid pressure acting on surfaces at both ends of the piston. One end of the piston is connected to a source of high pressure hydraulic fluid, while the other end of the piston can be connected to a source of high pressure hydraulic fluid or a source of low pressure hydraulic fluid, under the control of a rotary hydraulic distributor coupled with solenoid valves.
Another engine valve actuating system is known in which each cylinder is provided with a coaxial venturi shaped duct having inwardly facing vanes that hold an electro-mechanical valve actuator. When the electro-mechanical valve actuator receives a pulsed electrical signal, the actuator operates to reciprocate the valve.
While a camshaft driven intake or exhaust valve will typically open and close with a constant period as measured in crankshaft degrees, for any given engine load or rpm, there is a need for an indirect valve actuation system for internal combustion engines that can operate more rapidly, and that will open the valve at the same rate regardless of engine operating conditions. Ideally, a valve actuation system should match the optimum, maximum valve rate of operation at maximum speed of operation of an engine to provide a rapid, optimum valve operation rate. It would also be desirable to provide a valve actuation system for internal combustion engines offering a speed of operation that will allow greater flexibility in programming valve events, resulting in improved low speed torque, lower emissions, and better fuel economy. Conventional approaches to providing higher rates of valve opening and closing have used non-latching control valves commonly involving systems using either spool valves or poppet valves, neither of which provide for a high flow open area in a small, low inertia system or energy efficient latching mechanisms. It would be desirable to provide a valve actuation and control system with an electro-hydraulic valve system, having a high flow open area, low inertia of operation, a small size, and ease of manufacture. The present invention meets these needs.
Briefly, and in general terms, the present invention provides for an intake/exhaust (I/E) reciprocating valve actuation and control system for the cylinders of an internal combustion engine, comprising I/E poppet valves moveable between a first and second position; a source of pressurized hydraulic fluid; a hydraulic actuator including an actuator piston coupled to the poppet valve and reciprocating between a first and second position responsive to flow of the pressurized hydraulic fluid to the hydraulic actuator; an electrically operated hydraulic valve controlling flow of the pressurized hydraulic fluid to the hydraulic actuator, the electrically operated valve including a linear latching motor; and electronic control means generating electrical pulses to control the electrically operated valve. In one embodiment, the control means comprises a digital signal processor. In another embodiment, the control means comprises a computer and a plurality of sensors disposed in the engine for sensing engine variables, and optimizing performance of the reciprocating valve actuation and control system. In one aspect of the invention, the linear latching motor comprises a solenoid coil associated with a permanent magnet, wherein the coil is energized to create a central axial repelling magnetic field relative to the permanent magnet field, and to generate concentric repelling and attractive fields to produce secondary repelling and tertiary attractive forces on the permanent magnet. In another aspect of the invention, the permanent magnet coercive strength is protected with a shorted turn. An electrical pulse repels the permanent magnet causing movement to increase a magnetic gap in the linear latching motor, and upon termination of power the permanent magnet returns to the original position through the action of the attractive force of the permanent magnet. In one present embodiment, two solenoid coils and permanent magnets are placed in opposition, such that when one of the coils is energized, the permanent magnet assembly is repelled and moves toward and latches to the second coil assembly and remains there when the power is terminated.
The electrically operated valve controlling flow of the pressurized hydraulic fluid to the actuator supplies pressurized hydraulic fluid to the hydraulic actuator when electrically pulsed to a first position, and dumps pressurized hydraulic fluid to a system return when electrically pulsed to a second position. In one present embodiment, the linear latching motor comprises a valve spool having a magnet carrier end formed of a non-magnetic material, such as a non-magnetic aluminum alloy, an inner pole piece and an outer pole piece having first and second ends, with the first ends of the inner pole piece and outer pole piece adjacent to the magnet carrier end of the spool valve, a coil disposed between the inner pole piece and the outer pole piece, and an outer sleeve surrounding the inner and outer pole pieces. A permanent magnet is mounted to the magnet carrier end of the valve spool, and a stop disk mounted to the second end of the inner pole piece, and the shorted turn is provided by the magnet carrier end of the valve spool. In one present aspect, the inner pole piece, outer sleeve, outer pole piece and stop disk are formed of a low carbon steel.
The hydraulic actuator comprises a self-contained cartridge assembly including an actuator piston having means for damping a stroke of the actuator piston to assure soft seating of the actuator, and to avoid overshoot of the actuator piston. In one present aspect, the means for damping comprises first damping means to avoid overshoot during an opening stroke of the engine valve, and may also comprise second damping means to decelerate the actuator piston to avoid high impact of the engine valve into the valve seat. In another aspect, the means for damping may comprise a stepped land on the actuator piston. The self-contained cartridge assembly may further comprise a main generally tubular sleeve having a bore, the bore having a surface defining a damper cavity, the actuator piston having a damper land member, and the damper cavity receiving the damper land member during an actuating stroke of the actuator piston, whereby hydraulic fluid is trapped in the damper cavity to damp motion of the actuator piston during a stroke of the actuator piston. The self-contained cartridge assembly may further comprise a secondary generally tubular sleeve having a bore, the secondary sleeve bore having a surface defining a secondary damper cavity, and the actuator piston having a surface defining a damper orifice for fluid communication of the hydraulic fluid from one of the main sleeve damping cavity and the secondary sleeve damping cavity to the hydraulic fluid return. When the self-contained cartridge assembly further comprises an alignment tube within which the main sleeve is disposed, a generally tubular damping spacer is disposed within the alignment tube adjacent to the main sleeve, a damping ring is disposed within the alignment tube adjacent to the damping spacer, the actuating piston having a surface defining a damping orifice for fluid communication of hydraulic fluid from the damper cavity to the hydraulic fluid return. In another aspect, the damper land member comprises a split ring, the split ring having a surface defining a damper orifice through the split ring for communicating hydraulic fluid to the hydraulic fluid return. The damper land member may comprise a laminar sealing ring, the sealing ring having a surface defining an orifice in the sealing ring for communication of hydraulic fluid to the hydraulic fluid return.
In a currently preferred embodiment, the source of pressurized hydraulic fluid comprises an engine-driven pump supplying engine oil under pressure as the hydraulic fluid, an accumulator is used to provide a reservoir of high pressure fluid, and an engine oil sump for receiving return hydraulic fluid. An unloader valve limiting pump output pressure is also provided, along with a check valve preventing backflow from the engine oil sump. An accumulator is also preferably provided for storing a sufficient volume of pressurized hydraulic fluid to moderate the pump and unloader valve duty cycle. The unloader valve preferably comprises a pressure sensing valve that senses pump output pressure and opens when the pressure reaches a preset value, so that when the unloader valve is open, flow from the pump returns to the engine oil sump.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.